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<H3>pair_style coul/diel command 
</H3>
<P><B>Syntax:</B>
</P>
<PRE>pair_style coul/diel cutoff 
</PRE>
<P>cutoff = global cutoff (distance units)
</P>
<P><B>Examples:</B>
</P>
<PRE>pair_style coul/diel 3.5
pair_coeff 1 4 78. 1.375 0.112 
</PRE>
<P><B>Description:</B>
</P>
<P>Style <I>coul/diel</I> computes a Coulomb correction for implict solvent
ion interactions in which the dielectric perimittivity is distance dependent.
The dielectric permittivity epsilon_D(r) connects to limiting regimes: 
One limit is defined by a small dielectric permittivity (close to vacuum)
at or close to contact seperation between the ions. At larger separations
the dielectric permittivity reaches a bulk value used in the regular Coulomb
interaction coul/long or coul/cut.
The transition is modeled by a hyperbolic function which is incorporated
in the Coulomb correction term for small ion separations as follows
</P>
<CENTER><IMG SRC = "Eqs/pair_coul_diel.jpg">
</CENTER>
<P>where r_me is the inflection point of epsilon_D(r) and sigma_e is a slope
defining length scale. C is the same Coulomb conversion factor as in the
pair_styles coul/cut, coul/long, and coul/debye. In this way the Coulomb
interaction between ions is corrected at small distances r. The lower 
limit of epsilon_D(r->0)=5.2 due to dielectric saturation <A HREF = "#Stiles">(Stiles)</A> 
while the Coulomb interaction reaches its bulk limit by setting 
epsilon_D(r->\infty)=epsilon, the bulk value of the solvent which is 78 
for water at 298K.  
</P>
<P>Examples of the use of this type of Coulomb interaction include implicit 
solvent simulations of salt ions 
<A HREF = "#Lenart">(Lenart)</A> and of ionic surfactants <A HREF = "#Jusufi">(Jusufi)</A>.
Note that this potential is only reasonable for implicit solvent simulations
and in combiantion with coul/cut or coul/long. It is also usually combined
with gauss/cut, see <A HREF = "#Lenart">(Lenart)</A> or <A HREF = "#Jusufi">(Jusufi)</A>.  
</P>
<P>The following coefficients must be defined for each pair of atom
types via the <A HREF = "pair_coeff.html">pair_coeff</A> command as in the example
above, or in the data file or restart files read by the
<A HREF = "read_data.html">read_data</A> or <A HREF = "read_restart.html">read_restart</A>
commands:
</P>
<UL><LI>epsilon (no units)
<LI>r_me (distance units)
<LI>sigma_e (distance units) 
</UL>
<P>The global cutoff (r_c) specified in the pair_style command is used.
</P>
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<P><B>Mixing, shift, table, tail correction, restart, rRESPA info</B>:
</P>
<P>This pair style does not support parameter mixing. Coefficients must be given explicitly for each type of particle pairs. 
</P>
<P>This pair style supports the <A HREF = "pair_modify.html">pair_modify</A> shift
option for the energy of the Gauss-potential portion of the pair
interaction.
</P>
<P>The <A HREF = "pair_modify.html">pair_modify</A> table option is not relevant
for this pair style.
</P>
<P>This pair style does not support the <A HREF = "pair_modify.html">pair_modify</A>
tail option for adding long-range tail corrections to energy and
pressure.
</P>
<P>This pair style can only be used via the <I>pair</I> keyword of the
<A HREF = "run_style.html">run_style respa</A> command.  It does not support the
<I>inner</I>, <I>middle</I>, <I>outer</I> keywords.
</P>
<P><B>Restrictions:</B>
</P>
<P>This style is part of the "user-misc" package.  It is only enabled
if LAMMPS was built with that package.  See the <A HREF = "Section_start.html#2_3">Making
LAMMPS</A> section for more info.
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "pair_coeff.html">pair_coeff</A>
<A HREF = "pair_gauss.html">pair_style gauss/cut</A>
</P>
<P><B>Default:</B> none
</P>
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<A NAME = "Stiles"></A>

<P><B>(Stiles)</B> Stiles , Hubbard, and Kayser, J Chem Phys, 77,
6189 (1982).
</P>
<A NAME = "Lenart"></A>

<P><B>(Lenart)</B> Lenart , Jusufi, and Panagiotopoulos, J Chem Phys, 126,
044509 (2007).
</P>
<A NAME = "Jusufi"></A>

<P><B>(Jusufi)</B> Jusufi, Hynninen, and Panagiotopoulos, J Phys Chem B, 112,
13783 (2008).
</P>
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